Thread: So why is it called a 3-way (or a 4-way)?

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So why is it called a 3-way (or a 4-way)?

Originally Posted by buzzbar
This is similar to the situation when you have to correct a homeowner when he incorrectly calls a 3-way switch, a 2-way switch. I've explained the reason numerous times, but they just seem to always get glassy-eyed after I tell them why it's a 3-way switch.
Originally Posted by Joethemechanic
Ya know, that one has been bothering me for at least 35 years. And if there are 3, it's called a 4 way. Somtin ain't right there. What gives?
Originally Posted by Dennis Alwon
We can add another 200 posts by asking why we call a switch that is located in 2 places a 3 way switch. Let's not go there...
I'll bite:
Why is a SPDT called a 3-way?

Why is a DPDT with an internal cross connect called a 4-way?

Other than, "That's just the way we do it", I don't have a clue.

ice

2. (I stole this from Bob)

One way is to just accept it, the other way takes 300 posts.

3. Actually, 'way' is an obscure ancient engineering term for 'terminal'.

Now does it make more sense?

4. OK, since this is the 'Instructors' section, I should probably be serious.

'Way' is used to indicate the amount of terminals, (ports) that are part of the switch (not including ground). It's the same in hydraulics and pneumatics. A '4-way' solenoid valve will have 4 ports for lines to connect to. Think about it, if there are four ways into the valve, wouldn't it make sense to call it a '4-way' valve? Early electrical designers just adopted the manner of description from the hydraulics field.

No matter how many switches are in a run, the ones with three terminals will be three-ways and the ones with four terminals will be four-ways.

When we use the standard definition of 'way', we think 'direction' or 'possibilities' and that is what makes the subject confusing. The definition we need to think of is 'passageway'.
Last edited by K8MHZ; 03-02-12 at 01:58 PM.

5. Originally Posted by K8MHZ
OK, since this is the 'Instructors' section, I should probably be serious.

'Way' is used to indicate the amount of terminals, (ports) that are part of the switch (not including ground). It's the same in hydraulics and pneumatics. A '4-way' solenoid valve will have 4 ports for lines to connect to.

No matter how many switches are in a run, the ones with three terminals will be three-ways and the ones with four terminals will be four-ways.

When we use the standard definition of 'way', we think 'direction' or 'possibilities' and that is what makes the subject confusing.
Hydraulics is just as confusing. What is called a three way valve IMO should still be called two way valve. Incoming media can leave one of two ways. Again IMO. What is called a four way valve IMO should be called a reversing valve (Heat pump manufacturers got this one right).

6. Originally Posted by kwired
What is called a three way valve IMO should still be called two way valve. Incoming media can leave one of two ways.
But that media arrived at the valve via a path that is different from the two it can take as it leaves the valve. There are three "ways" fluid can flow: In, Out-to-the-left, and Out-to-the-right.

7. Originally Posted by kwired
Hydraulics is just as confusing. What is called a three way valve IMO should still be called two way valve. Incoming media can leave one of two ways. Again IMO. What is called a four way valve IMO should be called a reversing valve (Heat pump manufacturers got this one right).
If you have had some training and experience in hydraulics you would find that it's not that confusing.

I remember starting out as a maint. tech in a foundry that a bunch of presses. Looking at the hydraulic schematics was like looking at hieroglyphics. I had a grumpy boss that knew all about the valves and started teaching me about them. I also went to Parker-Hannefin's course on industrial hydraulics. After that, I could look at the schematics and know exactly what I was looking at.

It's really not rocket surgery.

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Originally Posted by K8MHZ
OK, since this is the 'Instructors' section, I should probably be serious.

'Way' is used to indicate the amount of terminals, (ports) that are part of the switch (not including ground). It's the same in hydraulics and pneumatics. A '4-way' solenoid valve will have 4 ports for lines to connect to. Think about it, if there are four ways into the valve, wouldn't it make sense to call it a '4-way' valve? Early electrical designers just adopted the manner of description from the hydraulics field.

No matter how many switches are in a run, the ones with three terminals will be three-ways and the ones with four terminals will be four-ways.

When we use the standard definition of 'way', we think 'direction' or 'possibilities' and that is what makes the subject confusing. The definition we need to think of is 'passageway'.
Interesting explanation. I also am involved in hydraulics from time to time, but I never thought about the connection to electrical terms. Makes sense. In the hydraulic world the terms always seemed intuitive, but now that you mention it I see the connection to 3 and 4 way switches.

9. Originally Posted by texie
Interesting explanation. I also am involved in hydraulics from time to time, but I never thought about the connection to electrical terms. Makes sense. In the hydraulic world the terms always seemed intuitive, but now that you mention it I see the connection to 3 and 4 way switches.
I probably would have stayed with hydraulics except they are so nasty to work on. And, they CAN kill you. We ran intensifiers that could deliver 11,000 psi into a 1 inch pipe or hose. Working pressure was 5 to 6 thousand. I saw a hose blow up that would have cut a person in half one day.

I remember coming to work one day wearing a brand new pair of steel toed work boots. I was on second shift taking over for first. I was helping about three other guys trying to pull off a 4 inch fitting from the bottom of a die cast unit. Finally, when it broke loose, about 35 gallons of glycol based hydraulic fluid came shooting out, soaking one of my boots, actually immersing it, with glycol.

Glycol doesn't evaporate like water does.

10. Originally Posted by K8MHZ

No matter how many switches are in a run, the ones with three terminals will be three-ways and the ones with four terminals will be four-ways.
post #5. Yes...

Can we talk about switches in a run now? eg. system?

Actually can you talk.............I'll listen...........?

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